Microsystem technology applications are often composed of two or more patterned substrates that are aligned and then bonded to each other. Wafer-to-wafer or two-substrate bonding is used to form micromechanical structures in such applications.
Thus the wafers are aligned in an alignment tool using either image capture, visible or IR alignment methods. Once aligned, the wafers are held in place by a removable clamping fixture that has two more clamps that clamp the edges of the wafers to spacer members to hold the wafers a desired distance apart. That is, the spacers keep the wafers face-to-face but separated by a few microns.
After the wafers are aligned, they are locked in a clamping fixture and moved to a separate bonding machine. Once in the bonding machine, a center or interior point contact is made to hold the wafers together at least at the contact point. The clamps are then removed and the spacer retracted and bonding of the wafer pair begins. However, there are drawbacks in the above prior art method. That is, the applying of the clamping fixture invariably allows some movement when clamping force is applied. Also, particles often result from the withdrawal of the mechanical spacers, a chronic problem.
Also, during transfer to a bonding chamber, the clamping fixture is subject to mechanical transfer forces and temperature variations which can affect the wafer alignment.
Then, in the bonding chamber, a vacuum is usually applied which causes turbulence and can add more particles between wafers before they are sealed together.
Accordingly there is need and market for method & apparatus for preserving wafer alignment from the alignment stage to the bonding stage of such wafers while avoiding or minimizing the chance for particles to become embedded between wafers before the bonding step is complete.
There has now been discovered method and apparatus for preserving wafer alignment and bonding of such wafers while minimizing particle intrusion therebetween, as further described below.